The present invention relates generally to containers for heating or cooling materials such as food, beverages, medicines, and the like and, more specifically, to a container that includes an internal module that adds heat to or removes heat from the materials in the surrounding container.
Containers may have integral modules for warming materials in the container, such as Japanese sake, coffee, or soup. Examples of such self-heating containers are disclosed in U.S. Pat. No. 4,640,264, issued to Yamaguchi et al., and U.S. Pat. No. 4,784,113, issued to Nagai et al. Such containers typically include an outer can or body, in which the food or beverage is sealed, and an inner can or module that contains two chemical reactants. The reactants are stable when separated from one another but, when mixed, produce an exothermic reaction. It is known that combinations of other reactants will produce endothermic reactions to cool the container contents.
The inner can is typically disposed adjacent one end of the container body. The inner can has two chambers, each of which contains one of the chemical reactants, separated by a breakable barrier such as metal foil or a thin plastic film. Typically, one of the reactants is in solution, and the other is in a solid powdered or granular form. A rod extends into the outer can at the end adjacent the inner can. One end of the rod is adjacent to the barrier, and the other end terminates in a button outside the outer can. To initiate the reaction that warms or cools the contents of the outer can, the can is disposed with that end upright. Depressing the button forces the rod downward, breaking the barrier and allowing the liquid reactant to drop into the solid reactant. The end of the rod may have a flared head to facilitate complete puncturing of the barrier. The heat produced by the resulting exothermic reaction or used by the resulting endothermic reaction is transferred between the inner can and the contents of the outer can by conduction. Exothermic reactions also typically generate a gas, which is allowed to escape through vents in the end of the container. When the reaction has stopped, the container is inverted. The second end of the outer can has a seal, such as pull-tab, that may be opened and through which the user may consume the heated contents.
Self-heating and self-cooling containers known in the art are uneconomical to manufacture because the mechanism for puncturing the foil barrier commonly has multiple components. The inner can contains the solid reactant and has a short, tubular cap sealing one end. The cap contains the liquid reactant. One end of the cap is sealed with the foil barrier, and the rod extends through an opening in the other end of the cap. Depressing the button forces the rod to slide in the opening until it punctures the foil barrier. Practitioners in the art have found that forcing a rod through the foil opens a large passage through which the liquid reactant can flow, thereby minimizing the time required for the liquid to drain from the cap into the remainder of the inner can. However, fabricating and assembling the multiple components increases the cost of the container. Furthermore, liquid can leak between the rod and the opening in the cap through which the rod moves. Practitioners in the art have therefore disposed a ring of wax around the rod where it exits the inner can to improve sealing. The step of adding the wax, however, increases the manufacturing complexity and, ultimately, cost of the container. Self-heating and self-cooling containers known in the art may also leak the powdery material that is the product of the completed reaction through the vents when the container is inverted.
The inner can may be unitarily formed with the outer can, as illustrated, for example, in U.S. Pat. No. 3,970,068, issued to Sato, and U.S. Pat. No. 5,088,870, issued to Fukuhara et al. The unitary container body is formed by providing a metal cylinder that is open at one end and closed at the other, and punching or deep-drawing a cavity in the closed end. A cap containing the liquid reactant is attached to the open end of the cavity.
After a self-heating container has been activated and the contents heated or cooled, heat transfer through the container wall rapidly equalizes the temperature of the contents with the environmental temperature. Thus, a heated beverage, for example, may cool undesirably before the user consumes it.
It would desirable for a user to know the length of time after activation the contents of a self-heating container will have reached a certain temperature. For example, it may be desirable to assure a user that a container having coffer will have reached 150 degrees Fahrenheit three minutes after activating the container. Nevertheless, the time between activation of a self-heating or self-cooling container and the onset of the chemical reaction is typically inconsistent, varying from container to container by seconds or even minutes due to variations in the composition of the reactants and the conditions under which they were manufactured. For example, it is known that the characteristics of quicklime (calcium oxide) may vary from manufacturer to manufacturer and even from batch to batch depending on moisture and temperature of the environment in which the quicklime is manufactured. Most commercially available quicklime is manufactured for use in cement for the construction trade. Because building contractors and masons do not need to precisely time of the onset of cement curing, manufacturers of calcium oxide typically do not exercise precise control over manufacturing variables such as environmental moisture and temperature.
It would be desirable to provide a self-heating or self-cooling container that has a minimal number of separate parts and can be economically manufactured. It would also be desirable to provide such a container with improved vent sealing to prevent leakage of powdery reaction products. It would further be desirable to provide such a container that begins the reaction at a consistent time after activation and that maintains its contents at the desired temperature for an extended period of time after the reaction is completed. These problems and deficiencies are clearly felt in the art and are solved by the present invention in the manner described below.